Effects on Pulp Yield and Properties Using Modified Pulping Procedures Involving Sulfur Profiling and Green Liquor Pretreatment

摘要

Using black liquor gasification (BLG), the recovered entities of sodium and sulfur can be split into two separate fractions with varying degrees of separation dependent on the operating conditions and the technology used. The separation of these chemicals creates some opportunities in the pulping process where chemical profiling may be employed to increase the pulp yield or to extend delignification. This benefit may be offset by an increase in the causticizing load. Of the various pulping options with black liquor gasification, sulfur profiling would be the lowest capital cost process to implement, especially for mills with a modified continuous or batch process. Previous process simulation work showed that BLG implementation alone would likely increase the cost of pulping operations due to the higher costs associated with limekiln operation. However, it was also found that by combining BLG implementation with pulping process modifications like split sulfidity pulping or green liquor pretreatment, the overall operational costs associated with pulping and chemical recovery could be substantially decreased. The work described here explores the possibilities made available for modified continuous cooking through the implementation of black liquor gasification. Laboratory pulping protocols were developed for modified continuous cooking, split sulfidity and green liquor pretreatment pulping. The obtained results indicate that the split sulfidity protocol can potentially be used to produce kraft pulps with higher yield, viscosity and strength properties relative the simulated MCC protocol; whereas the green liquor pretreatment protocol can be used to produce pulps with yields similar to the MCC protocol, but with higher viscosity and strength properties. Moreover, significant cost savings can be realized by using the green liquor pretreatment approach in place of the MCC protocol, as the load on the recaust system and particularly the limekiln would be reduced.